1. Technical Field
The present disclosure relates to a semiconductor device and a method for manufacturing the semiconductor device, and particularly to a semiconductor device for high voltages and large currents, and a method for manufacturing the semiconductor device.
2. Description of the Related Art
Silicon carbide (SiC) is a semiconductor material having a larger band gap and higher dielectric breakdown electric field strength as compared to silicon (Si), and is expected to be applied to next-generation low-loss power devices etc. SiC includes many polytypes such as cubic 3C-SiC, and hexagonal 6H-SiC and 4H-SiC.
As a typical switching element for power devices using SiC, mention is made of a field effect transistor such as a metal insulator semiconductor field effect transistor (hereinafter, abbreviated as a “MISFET”) or a metal semiconductor field effect transistor (hereinafter, abbreviated as a “MESFET”). The switching element is capable of switching between an on-state in which a drain current of several amperes (A) or more passes and an off-state in which a drain current does not pass, according to a voltage applied between a gate electrode and a source electrode. In an off-state, a high voltage of several hundred volts (V) can be achieved.
Enhancement of a device integration degree is effective for feeding a further large current in a power device such as a MISFET. Thus, a vertical power MISFET having a trench gate structure (hereinafter, abbreviated as a “trench-type MISFET”) as a structure that will replace a conventional planar gate structure has been proposed (e.g., Patent Literature 1). In the trench-type MISFET, a channel region is formed on a side wall portion of a trench formed in a semiconductor layer, and therefore a unit cell area can be reduced. As a result, a device integration degree can be improved.
A trench-type MISFET having a structure in which as a channel layer, a thin epitaxial layer is formed on a side wall portion of a trench has also been proposed.
On the other hand, Non-Patent Literature 1 describes that when a trench is formed in a 4H-SiC(0001) substrate with an off-angle of 8°, and silicon carbide is epitaxially grown in the trench, a (0001) facet plane may be generated on a main surface of the SiC substrate due to step flow growth of the silicon carbide.